To make the risotto, add a glug of oil to a large pan over a medium heat. Add the onions and cook until softened but not coloured. Meanwhile, heat the chicken stock in a pan over a low heat.
Add the rice to the onions and stir. Toast until the rice is extremely hot, then deglaze with the wine. Remove from the heat and allow to sit for 5 minutes.
Marinate the chopped anchovy fillets in the vinegar, garlic, olive oil and chopped parsley. Set aside.
Return to the heat, add 2 ladles of stock and bring to the simmer while stirring continuously, until the stock has been absorbed. Keep cooking like this, adding one ladle of stock at a time, until it is all soaked up.
Pour in the passata and continue cooking, adding a little more water if necessary, until it has been absorbed and the rice is cooked through. Beat in the cubed butter and grated Parmesan and remove from the heat – it should be nice and glossy.
Serve the risotto and pour the marinated anchovies all over the top – this will have a large amount of oil over the top but it is key to the finishing off the dish, so do not skimp!